Field
The present disclosure relates generally to the field of energy storage devices, and more particularly, to a parallel battery module.
Background
When a battery is over-charged, the internal heat production and internal pressure of the battery are increased due to the decomposition of the battery electrolyte, which may lead to fire or explosion. As shown in FIG. 1, the structure commonly used by the industry right now to address over-charging is a combination of a conducting deformable piece 17 and a fuse 16. When the battery cell is over-charged and the internal gas pressure reaches a certain level, the conducting deformable piece 17 deforms such that a first terminal 12 is electrically connected to a conducting top cover plate 11 via a conducting connector 13. Because a second terminal 14 is electrically connected to the conducting top cover plate 11, an external short circuit can be formed between the first terminal 12 and the second terminal 14, thereby protecting the battery. When the current generated by the external short circuit is too high, it is likely to melt the conducting deformable piece 17. When the conducting deformable piece 17 is melted, the electrolyte inside the bare cell 15 will be ejected from the position of the conducting deformable piece 17 and in contact with the air. And at the same time, a high temperature is resulted due to the melting, which may cause a fire at the location of the conducting deformable piece 17, leading to a safety breach. To prevent the conducting deformable piece 17 from being melted, a fuse 16 is provided at the side of the second terminal 14 that is in connection with the bare cell 15. As a result, when the external short circuit is formed between the first terminal 12 and the second terminal 14 to consequently generate a high current, the fuse 16 is blown, which prevents the battery cell 1 from being continuously charged to cause a danger of fire or explosion, while ensuring that the conducting deformable piece 17 is not melted.
Such a solution may solve the problem that a battery cell is over-charged or a battery module with multiple battery cells in series connection is over-charged. However, said solution cannot solve the problem that a battery module with multiple battery cells in parallel connection is over-charged. Referring to FIG. 1 and FIG. 6, when the battery cell 1 is over-charged and gas is produced, the conducting deformable piece 17 of a battery cell deforms. The first terminal 12 and the second terminal 14 of said battery cell 1 are connected and become equivalent to one single wire. This battery cell 1 forms an external short circuit on its own. Moreover, other battery cells in parallel will also form external short circuits through the conducting top cover plate 11 of this battery cell 1. As a result, the current flowing through the conducting top cover plate 11 and the conducting deformable piece 17 of this battery cell 1 is a sum of currents of all parallel battery cells, while the fuse 16 of each battery cell 1 only withstands its own current. Consequently, the conducting deformable piece 17 of said battery cell 1 may melt prior to the fuse 16. Thus, the connection of said battery cell 1 and the main charging circuit cannot be broken, leading to failure of the bare cell 15 of said battery cell 1 due to continuous charging.
In such a circumstance, the overcurrent cross sectional area of a single conducting deformable piece 17 may need be greater than the overcurrent cross sectional area of the fuse 16. The overcurrent cross sectional area of the fuse 16 cannot be too small given the reliability requirement of the fuse 16 during a normal current and the strength requirement of the fuse 16 itself. The overcurrent cross sectional area of the fuse 16 of a battery cell used by the industry at present is typically 3 to 8 mm2.
If the overcurrent cross sectional area of the fuse 16 is 4 mm2, in an example of three battery cells in parallel connection, when a battery cell 1 is subject to external short circuit, the conducting deformable piece 17 of said battery cell 1 withstands the external short circuit current 3I applied by the three battery cells, while the fuse 16 only withstands the external short circuit current I of one single battery cell. As a result, the overcurrent cross sectional area of the conducting deformable piece 17 needs to be more than three times of that of the fuse 16, namely at least 12 mm2. Due to the restriction by the battery size, however, the lengthwise and widthwise sizes of the conducting deformable piece 17 are restricted, and the overcurrent cross sectional area of the conducting deformable piece 17 cannot be infinitely enlarged.
Similarly, for a battery module with four or more battery cells in parallel connection, the overcurrent cross sectional area of the conducting deformable piece 17 may need to be greater than 16 mm2, which may be difficult to accommodate due to the restriction by the battery size.